- 2062 Baisakh (old course) · 2 marks
Colour versus streak of mineral
Short answer
Colour is the bulk appearance in reflected light, variable due to impurities. Streak is the constant powder colour obtained by rubbing on a porcelain plate, reliable for minerals softer than 6.5; e.g., hematite streak is always red-brown regardless of its external colour.
Differentiate between colour and streak of a mineral.
| Basis | Colour | Streak |
|---|---|---|
| Meaning | Appearance of the mineral in bulk, in reflected light | Colour of the fine powder of the mineral |
| How observed | By eye on the specimen | By rubbing on unglazed porcelain plate |
| Constancy | Variable; changes with impurities and weathering | Constant for a mineral |
| Reliability | Low | High |
| Applies to | All minerals | Minerals softer than the plate (below 6.5) |
| Example | Hematite may be grey, black or red | Always red-brown streak |
| Quartz | Varied colours | White (colourless) |
✓ Answer checked by Claude Opus 5.5 (high effort)
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